The term "latex" was originally applied to aqueous dispersions of natural rubber. This term is now used in the art to refer to aqueous dispersions of natural rubber, aqueous dispersions of synthetic polymers, such as elastomeric polymers, and mixtures thereof.
Latex has a wide variety of uses in the textile field. For instance, latex can be used for laminating textiles, e.g., carpeting. In the manufacture of carpeting, particularly tufted carpeting, it is the general practice to coat the back of the carpet with a latex formulation. In this case the coating acts as an adhesive to secure the tufts in place so that they are not pulled out in normal use. A secondary fabric backing or layer is sometimes applied to carpeting. Materials used for this purpose are woven jute, or a woven or non-woven textile made of such synthetic materials as polypropylene, rayon, viscose, nylon, polyester, acrylics or mixtures thereof. The principal purpose of this secondary backing or layer is to provide additional dimensional stability and stiffness to the carpet. The secondary layer is generally laminated to the carpet by the use of a latex formulation or composition.
The latex-starch composition used in the present method may be applied in the manufacture of tufted carpets and other composite textile such as woven carpets; upholstery fabrics; curtaining fabrics; needlefelt carpets; lightweight laminated fabrics including apparel fabrics; and non-woven fabrics, for such purpose as providing improved weight, handle, drape or opacity to the composition textile, in addition to improved strength and durability and dimensional stability.
The rheological behavior of a latex composition is quite important in regard to the properties that such will impart to a textile composite. For instance, if the viscosity of the composition is excessive, the latex will not penetrate sufficiently into the textile to provide the desired adhesiveness between the tufts and the primary backing and among the fibers of the tufting thread. On the other hand, if the viscosity of the latex is too low, excessive penetration through the textile takes place so that latex is not disposed at a point where it will provide the desired degree of adhesiveness to the secondary backing. In the textile field, the penetration capability of a latex is referred to as "ride." A latex which is considered to give a "high ride" is one which will not penetrate excessively into or through the weave of a textile fabric but will, nevertheless, flow sufficiently into the interstices of the textile to provide the desired adhesive strength.
A latex composition which is to be utilized for forming a textile composite must develop adhesiveness as early in the drying curing process as possible to minimize displacement of the secondary backing through mechanical movement. This property is generally referred to in the textile art as "early bonding" or "green strength."
A wide variety of latices have been utilized for preparing textile composites. For example, cis-polyisoprene latices, natural rubber latices, mixtures of natural latices with cold SBR latices and other synthetic latices have been used. Carboxylated butadiene-containing latices are quite often used for this purpose since they require little, if any, separate curing agents. Such latices do, however, have to be dried or cured by the application of heat at a temperature below the thermal degradation temperature of the textiles to which they are applied.
Elastomeric or flexible polymers in which the polymer chain contains various functional groups pendant from the chain exhibit the desired low-temperature curability without the addition of other ingredients. Such polymers may be made by the emulsion interpolymerization of a conjugated diene, such as butadiene, with, inter alia, an ethylenically unsaturated functional monomer such as an .alpha.,.beta.-unsaturated carboxylic acid, unsaturated dicarboxylic acids, mono-esters of such dicarboxylic acids, acrylamides and N-methylolacrylamides. In addition to the conjugated diene and the functional monomer, the polymerization mixture may also contain a secondary copolymerizable monomer such as styrene, acrylonitrile, methyl methacrylate, vinylidene chloride and the like.
The relative amount of secondary copolymerizable monomer determines in large part the functional characteristics of the latex and its effect on the textile to which it is applied. A latex composition containing relatively large amounts of secondary monomer will impart a stiff hand to the textile, whereas, a latex containing relatively low amounts of secondary monomer will impart a softer hand, i.e., more flexibility to the laminated textile. It is well within the purview of those skilled in the art to devise a polymer to meet the desired characteristics by adjustment of the amount of secondary monomer. For example, a latex copolymer containing about 45 weight percent styrene monomer may not impart the desired degree of stiffness. On the other hand, a latex copolymer containing about 65 weight percent styrene monomer yields a polymer which may impart stiffness to an undesirable degree. However, these latices may be blended in various proportions to produce a latex mixture which, when applied to a textile, imparts stiffness to an intermediate degree.
Latex compositions used for laminating textiles generally contain large amounts of finely divided inorganic filler such as whiting (CaCO.sub.3), barytes, alumina, pigments and the like. These materials are added to impart certain secondary properties such as opacity, fire retardance, stiffness and color.
In addition to the above-referred primary functional components, latex compositions may also contain various additional components such as antioxidants, defoamers, plasticizers, bactericides, emulsifiers, thickeners, dispersants and the like.
U.S. Pat. Nos. 3,779,857 and 4,055,694 disclose granular starch-latex systems useful in the textile field. While these systems provide various benefits, they do not impart the desired degree of cohesiveness to a textile composite.